Insulinotropic peptide derivative with modified n-terminal charge

ABSTRACT

The present invention relates to an insulinotropic peptide derivative with a modified N-terminal charge and a pharmaceutical composition including the same. Specifically, the insulinotropic peptide derivative is characterized in that the N-terminal positive charge of the insulinotropic peptide is modified to a neutral or net negative charge at neutral pH. The insulinotropic peptide derivative according to the present invention is rapidly dissociated from the GLP-1 receptor owing to the above modification in the N-terminal charge, and exhibits enhanced insulinotropic ability and blood glucose-lowering activity compared to the native insulinotropic peptide while maintaining its stability in blood. Accordingly, the insulinotropic peptide derivative of the present invention is very useful for the treatment of type 2 diabetes.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 14/758,842 (allowed)filed Jul. 1, 2015, which is a National Stage of InternationalApplication No. PCT/KR2014/000025 filed Jan. 3, 2014, claiming prioritybased on Korean Patent Application No. 10-2013-0000766 filed Jan. 3,2013 and Korean Patent Application No. 10-2014-0000031 filed Jan. 2,2014, the contents of all of which are incorporated herein by referencein their entirety.

TECHNICAL FIELD

The present invention relates to an insulinotropic peptide derivativewhich is modified to have increased insulinotropic activity and bloodglucose level-lowering activity, and a pharmaceutical compositioncontaining the same. The insulinotropic peptide derivative according tothe present invention is characterized in that the N-terminal charge ofthe insulinotropic peptide is modified to a neutral or net negativecharge.

BACKGROUND ART

Peptides can be easily denatured due to their low stability, lose theiractivities via degradation by in-vivo proteolytic enzymes, and are sosmall so as to be easily removed through the kidney. Accordingly, inorder to maintain the blood levels and the titers of a pharmaceuticaldrug containing a peptide as a pharmaceutically active component, it isnecessary to frequently administer the peptide drug to a patient.

However, most peptide drugs are administered as injection preparationsand frequent administration is necessary for the maintenance of theblood level of the physiologically active peptides, thus causing asevere pain for the patients. To solve these problems, many efforts havebeen made to increase the stability of peptide drugs in blood and tomaintain the drugs in the blood at high level for a prolonged period oftime, thereby maximizing the pharmaceutical efficacy of the drugs.

In particular, the long-acting preparations of such peptide drugstherefore need to increase their stability while simultaneouslymaintaining their titers at sufficiently high levels without causing anyimmune responses in patients. In this regard, as methods for stabilizingthe peptides, and inhibiting the degradation by a proteolytic enzyme,attempts have been made to modify specific amino acid sequences whichare sensitive to proteolytic enzymes.

For example, GLP-1 (7-37 or 7-36 amide), which has a therapeutic effectof lowering the blood glucose level for treating type 2 diabetes, has ashort physiological half-life of about 4 minutes or less, due to loss ofthe titers of GLP-1 through the cleavage between the 8th amino acid(Ala) and the 9th amino acid (Asp) by a dipeptidyl peptidase IV (DPPIV). In this regard, GLP-1 derivatives, in which Ala⁸ is substitutedwith Gly, Leu, or D-Ala to increase the resistance to DPP IV whilemaintaining the physiological activity, have been developed. Moreover,the N-terminal amino acid of GLP-1, His⁷, is critical for the GLP-1activity, and serves as a target for DPP IV. Accordingly, the N-terminusis modified to an alkyl or acyl group, and His⁷ is subjected toN-methylation or alpha-methylation, to increase its resistance to DPPIV, and to maintain its physiological activity. Although it wasconfirmed that the stability was improved due to an increase in theirresistance to DPP IV there was also a report that the receptor affinityof the derivatives obtained by modifying His⁷ was considerably reducedand the secretory capacity of cAMP was reduced at the same concentration(see, Gallwitz et al., Regulatory Peptide 79: 93-102, 1999; Gallwitz etal., Regulatory Peptide 86: 103-111, 2000).

In addition, among the insulinotropic peptides such as GLP-1, exendin-4is composed of a sequence of His-Gly instead of His-Ala, which is asequence of GLP-1 acting as a substrate for DDP IV. Accordingly,exendin-4 has resistance to DPP IV and higher physiological activitythan that of GLP-1. Thus, exendin-4 has a longer in-vivo half-life thanthat of GLP-1. However, although the in-vivo half-life of exendin-4 islonger than that of GLP-1, commercially available exendin-4 (exenatide)must be administered to a patient twice a day via injection, and this isa major inconvenience for patients.

Under these circumstances, the present inventors have made variousefforts to increase the activities and stability in blood ofinsulinotropic peptides and discovered that insulinotropic peptidederivatives with a modified N-terminal charge can exhibit superiorpharmacokinetics and higher insulinotropic activities compared to thoseof a native insulinotropic peptide, thereby completing the presentinvention.

DISCLOSURE Technical Problem

An objective of the present invention is to provide an insulinotropicpeptide derivative having increased insulinotropic activities and henceexcellent blood glucose level-lowering activities.

Another objective of the present invention is to provide apharmaceutical composition for the treatment of diabetes containing theabove insulinotropic peptide derivative as an active ingredient.

A further objective of the present invention is to provide a method fortreating diabetes using the above insulinotropic peptide derivative.

Technical Solution

In an aspect for accomplishing the above objectives, the presentinvention provides an insulinotropic peptide derivative in which theN-terminal charge of a native insulinotropic peptide is modified.

In an embodiment, the present invention provides an insulinotropicpeptide derivative in which the N-terminal amino group or N-terminalamino acid residue of the insulinotropic peptide is modified to have aneutral or net negative charge.

In another embodiment, the insulinotropic peptide derivative accordingto the present invention is characterized in that it is a chemicallymodified derivative in which the alpha-amino group of the N-terminalhistidine residue of the insulinotropic peptide is removed orsubstituted, or the alpha-carbon is removed, thereby having a neutral ornet negative charge.

In still another embodiment, the insulinotropic peptide derivativeaccording to the present invention is characterized in that thederivative is introduced with a chemical modification corresponding toat least one selected from the group consisting of: removing theN-terminal amino group of the insulinotropic peptide; substituting theN-terminal amino group with a hydroxyl group; modifying the N-terminalamino group with two methyl groups; substituting the N-terminal aminogroup with a carboxyl group; removing the alpha-carbon of the N-terminalhistidine residue thereby leaving only the imidazoacetyl group; andremoving the N-terminal amino group while substituting the C-terminalcarboxyl group with 3-amino propylamide.

In still another embodiment, the insulinotropic peptide derivativeaccording to the present invention is characterized in that theN-terminal histidine residue of insulinotropic peptide is substitutedwith a material selected from the group consisting of desamino-histidyl,dimethyl-histidyl, beta-hydroxy imidazopropionyl, 4-imidazoacetyl, andbeta-carboxyimidazopropionyl.

In still another embodiment, the insulinotropic peptide derivativeaccording to the present invention is characterized in that theN-terminal histidine residue of the insulinotropic peptide issubstituted with desamino-histidyl, and the C-terminal carboxyl group issubstituted with 3-amino propylamide.

In still another embodiment, the insulinotropic peptide derivativeaccording to the present invention is characterized in that theinsulinotropic peptide has binding activity with a GLP-receptor.

In still another embodiment, the insulinotropic peptide derivativeaccording to the present invention is characterized in that theinsulinotropic peptide is GLP-1 represented by SEQ ID NO: 1, exendin-4represented by SEQ ID NO: 2, exendin-3 represented by SEQ ID NO: 3,oxyntomodulin represented by SEQ ID NO: 5, GIP represented by SEQ ID NO:6, or an analogue thereof.

In still another embodiment, the insulinotropic peptide derivativeaccording to the present invention is characterized in that it has ahigher dissociation constant (Kd) from a GLP-1 receptor due to themodification in the N-terminal charge than that of a nativeinsulinotropic peptide.

In still another embodiment, the insulinotropic peptide derivative ofthe present invention is characterized in that the N-terminal histidineresidue of GLP-1, exendin-4, exendin-3, oxyntomodulin, GIP, or ananalogue thereof is substituted with desamino-histidyl,dimethyl-histidyl, beta-hydroxy imidazopropionyl, 4-imidazoacetyl, orbeta-carboxyimidazopropionyl.

In still another embodiment, the insulinotropic peptide derivative ofthe present invention is characterized in that the N-terminal histidineresidue of GLP-1, exendin-4, exendin-3, oxyntomodulin, GIP, or ananalogue thereof is substituted with desamino-histidyl, and theC-terminal carboxyl group of GLP-1, exendin-4, exendin-3, oxyntomodulin,GIP, or an analogue thereof is substituted with 3-amino propylamide.

In still another embodiment, the insulinotropic peptide derivative ofthe present invention is characterized in that it is selected from thegroup consisting of: desamino-histidyl-exendin-4 prepared by removingthe N-terminal amino group of exendin-4; beta-hydroxyimidazopropionyl-exendin-4 prepared by substituting the N-terminal aminogroup of exendin-4 with a hydroxyl group;beta-carboxyimidazopropionyl-exendin-4 prepared by substituting theN-terminal amino group of exendin-4 with a carboxyl group;dimethyl-histidyl-exendin-4 prepared by modifying the N-terminal aminogroup of exendin-4 with two methyl groups; and imidazoacetyl-exendin-4prepared by removing the alpha-carbon of histidine, which is the firstamino acid of exendin-4.

In still another embodiment, the insulinotropic peptide derivative ofthe present invention is characterized in that it isDA-exendin-4-propyl-amide prepared by removing the N-terminal aminogroup of exendin-4 while substituting the C-terminal carboxyl groupthereof with 3-amino propylamide.

In another aspect, the present invention provides a pharmaceuticalcomposition for the treatment of diabetes containing as an activeingredient the insulinotropic peptide derivative in which the N-terminalcharge of the insulinotropic peptide is modified as described above.

In still another embodiment, the present invention provides a method fortreating diabetes including administering a therapeutically effectiveamount of the insulinotropic peptide derivative, in which the N-terminalcharge is modified as described above, to a subject in need thereof.

Advantageous Effects

The insulinotropic peptide derivative with a modified N-terminal chargein accordance with the present invention can be rapidly dissociated fromthe GLP-1 receptor due to the modification in the N-terminal charge, soas to prevent clearance of the insulinotropic peptide and reducedesensitization. Also, the insulinotropic peptide derivative with amodified N-terminal charge according to the present invention canexhibit improvements of insulinotropic activity and in-vivo bloodglucose level-lowering activity due to a change in the binding activitywith the GLP-1 receptor compared to those of a native insulinotropicpeptide. Therefore, the insulinotropic peptide derivative according tothe present invention can be very effectively used for the treatment ofdiabetes.

DESCRIPTION OF DRAWINGS

FIG. 1a through 1e show coupling curves according to concentrations ofthe insulinotropic peptide derivative with a modified N-terminal chargeaccording to the present invention with GLP-1 receptors, wherein FIG. 1arepresents native exendin-4, FIG. 1b CA-exendin-4, FIG. 1c DA-exendin-4,Figure id DA-exendin-4-propyl-amide, and FIG. 1e HY-exendin-4.

FIG. 2 shows a result of measurement of insulinotropic activity ofnative exendin-4 and a CA-exendin-4 derivative with a modifiedN-terminal charge according to the present invention.

FIG. 3 shows a result of measurement of blood glucose level-loweringactivity of native exendin-4 and a CA-exendin-4 derivative with amodified N-terminal charge according to the present invention indiabetic animal models.

BEST MODE

The present invention provides an insulinotropic peptide derivativehaving a modification on its N-terminal charge.

The insulinotropic peptide derivative according to the present inventionis characterized by the modification of the N-terminal charge of theinsulinotropic peptide thereby rapidly dissociating it from thereceptor.

The term “insulinotropic peptide derivative” as used herein refers to aderivative in which the N-terminal positive charge of a nativeinsulinotropic peptide, its analogue or a fragment thereof is modifiedto a neutral or net negative charge by a chemical, genetic, or physicalmanipulation while retaining its unique insulinotropic function.

Specifically, the insulinotropic peptide derivative according to thepresent invention is preferably a derivative in which the N-terminalamino group or N-terminal amino acid residue of the insulinotropicpeptide is chemically modified to have a neutral or net negative charge,and more preferably, a derivative in which the positive charge on thefirst amino acid residue of the N-terminal of the insulinotropic peptideis modified to a neutral or net negative charge.

The term “insulinotropic peptide” as used herein refers to a peptidehaving an insulinotropic function for stimulating the synthesis andexpression of insulin in a pancreatic beta cell. Any insulinotropicpeptide suitable for the present invention may be used, withoutlimitation, as long as it shows physiological activity by binding with aGLP-1 receptor. Non-limiting examples thereof include GLP-1 (7-37) ofSEQ ID NO: 1, exendin-4 of SEQ ID NO: 2, exendin-3 of SEQ ID NO: 3,oxyntomodulin of SEQ ID NO: 5, a glucose-dependent insulinotropicpolypeptide of SEQ ID NO: 6, and an analogue or fragment thereof.

The term “insulinotropic peptide analogue” as used herein refers to apeptide in which at least one amino acid of an amino acid sequence of anative insulinotropic peptide is modified, and which has aninsulinotropic function. Preferably, the analogue of the insulinotropicpeptide of the present invention refers to a polypeptide showing atleast 80% amino acid sequence homology to that of the nativeinsulinotropic peptide, and it may be in a form wherein the amino acidresidues are partly chemically substituted (e.g., alpha-methylation,alpha-hydroxylation), removed (e.g., deamination), or modified (e.g.,N-methylation).

In a preferred embodiment of the invention, the insulinotropic peptideanalogue refers to showing equivalent or higher insulinotropic activitycompared to that of the native insulinotropic peptide, but the range ofthe insulinotropic peptide analogues of the present invention is notnecessarily limited to those having the insulinotropic activity at thislevel.

The term “fragment of an insulinotropic peptide” according to thepresent invention refers to a fragment having at least one amino acidadded or removed at the N-terminus or the C-terminus of the nativeinsulinotropic peptide while retaining the insulinotropic function. Theadded amino acid may be a non-naturally occurring amino acid (e.g.,D-type amino acid).

GLP-1 is a hormone secreted by the small intestine, and usually promotesbiosynthesis and secretion of insulin, inhibits glucagon secretion, andpromotes glucose uptake by the cells. In the small intestine, a glucagonprecursor is decomposed into three peptides, i.e., glucagon, GLP-1, andGLP-2. Here, the GLP-1 refers to GLP-1 (1-37), which is in the formwithout an insulinotropic function, and is processed to become an activeform of GLP-1 (7-37). The GLP-1 (7-37) has an amino acid sequencerepresented by SEQ ID NO: 1.

Preferably, a GLP-1 analogue may be selected from the group consistingof Arg³⁴-GLP-1(7-37), Gly⁸-GLP-1(7-36)-amide, Gly⁸-GLP-1(7-37),Val⁸-GLP-1(7-36)-amide, Val⁸-GLP-1(7-37), Val⁸Asp²²-GLP-1(7-36)-amide,Val⁸Asp²²-GLP-1(7-37), Val⁸Glu²²-GLP-1(7-36)-amide,Val⁸Glu²²-GLP-1(7-37), Val⁸Lys²²-GLP-1(7-36)-amide,Val⁸Lys²²-GLP-1(7-37), Val⁸Arg²²-GLP-1(7-36)-amide,Val⁸Arg²²-GLP-1(7-37), Val⁸His²²-GLP-1(7-36)-amide,Val⁸His²²-GLP-1(7-37), Val⁸Trp¹⁶Glu²²-GLP-1(7-37),Val⁸Glu²²Val²⁵-GLP-1(7-37), Val⁸Tyr¹⁶Glu²²-GLP-1(7-37),Val⁸Trp¹⁶Glu²²-GLP-1(7-37), Val⁸Leu¹⁶Glu²²-GLP-1(7-37),Val⁸Tyr¹⁸Glu²²-GLP-1(7-37), Val⁸Glu²²His³⁷-GLP-1(7-37),Val⁸Glu²²Ile³³-GLP-1(7-37), Val⁸Trp¹⁶Glu²²Val²⁵Ile³³-GLP-1(7-37),Val⁸Trp¹⁶Glu²²Ile³³-GLP-1(7-37), Val⁸Glu²²Val²⁵Ile³³-GLP-1(7-37), andVal⁸Trp¹⁶Glu²²Val²⁵-GLP-1(7-37), but is not limited thereto.

As another type of insulinotropic peptide, exendin-4 is a polypeptideconsisting of 39 amino acids that shows 53% amino acid sequencesimilarity with GLP-1 and has an amino acid sequence represented by SEQID NO: 2. Exendin-3 has an amino acid sequence represented by SEQ ID NO:3 and it is an exendin-4 analogue wherein only amino acids at positions2 and 3 differ from exendin-4. Exendin-3 is one in which amino acids atpositions 2 and 3 of exendin-4 are substituted with serine and asparticacid, respectively, and it can be represented bySer²Asp³-exendin-4(1-39). As another exendin-analogue, ZP-10, in whichamino acids at positions 38 and of exendin-4 are substituted with serineand lysine, respectively, is represented asSer³⁸Lys³⁹-exendin-4(1-39)-LysLysLysLysLys-amide and has an amino acidsequence of SEQ ID NO: 4.

Oxyntomodulin refers to a peptide produced from a pre-glucagon, which isa precursor of glucagon, and is released from L-cells of the smallintestine in proportion to the nutrient uptake along with GLP-1.Oxyntomodulin is a peptide hormone consisting of 37 amino acidsrepresented by SEQ ID NO: 5, and shows the effects of food intakeinhibition, satiety enhancement, and lypolysis of glucagon.

The glucose-dependent insulinotropic peptide (GIP) is an incretin thatregulates insulin secretion in the pancreas in a glucose-dependentmanner in response to intestinal absorption of nutrients. The GIPconsists of 42 amino acids described in SEQ ID NO: 6 and is secretedfrom the cell K of the small intestine. GIP not only stimulates insulinsecretion in a glucose-dependent manner but also promotes insulinsynthesis, induces proliferation of β-cells, and inhibits apoptosis.

The methods used for manufacturing a native insulinotropic peptide, itsanalogue, or a fragment thereof as described above may be usedindependently or in combinations thereof. For example, an insulinotropicpeptide, which differs in at least one amino acid residue of an aminoacid sequence from that of the native insulin and has deamination at theN-terminal amino acid residue, is included in the present invention.

In a specific embodiment, the native insulinotropic peptide and themodified insulinotropic peptide derivative used in the present inventionmay be synthesized by a solid phase synthesis protocol, and most nativepolypeptides including the native insulinotropic peptide may also beproduced by recombinant methods.

The GLP-1, exendin-4, exendin-3, oxyntomodulin, or GIP analogue mayrefer to a peptide, in which at least one amino acid of the nativeGLP-1, exendin-4, or exendin-3 is substituted, removed, and/or added; orat least one amino acid residue is chemically modified, e.g., byalkylation, acylation, esterification, or amidation, and has the nativeinsulinotropic activity.

Concerning GLP-1 and exendin-3 or exendin-4 analogues, InternationalPublication WO97/046584 discloses exendin analogues, in which theC-terminal end of GLP-1 or exendin-4 is partially removed or substitutedwith a non-natural amino acid, i.e., norleucine; and InternationalPublication WO99/07404 discloses exdendin agonist compounds withsubstitution of amino acids of exendin including non-natural aminoacids, such as pentylglycine, homoproline, and tert-butylglycine; and USPatent Application Publication No. 2008/0119390 discloses exendinagonist compounds in which exdendin-4 is configurated to have a shorteramino acid sequence than the native type or substituted with other aminoacids, the entire contents of which are incorporated herein byreference.

The insulinotropic peptide derivative according to the present inventionis characterized in that the N-terminal amino group or N-terminal aminoacid residue of the native insulinotropic peptide, its analogue, or afragment thereof is modified to have a neutral or net negative charge asdescribed above.

Preferably, the insulinotropic peptide derivative according to thepresent invention is characterized in that the positive charge on thefirst amino acid residue of the N-terminal of the insulinotropic peptideis chemically modified to a neutral or net negative charge.

The insulinotropic peptide derivative in which the N-terminal positivecharge of the insulinotropic peptide is chemically modified to a neutralor net negative charge according to the present invention ischaracterized in that it has a higher dissociation constant (Kd) fromthe GLP-1 receptor compared to that of the native insulinotropicpeptide. The insulinotropic peptide derivative according to the presentinvention is modified to have preferably a more than two-fold, morepreferably a more than three-fold and most preferably a more thansix-fold higher dissociation constant from the GLP-1 receptor comparedto that of the native insulinotropic peptide, but is not limitedthereto.

The insulinotropic peptide derivative, in which the N-terminal positivecharge of the insulinotropic peptide is modified to a neutral or netnegative charge according to the present invention, may be produced byvarious methods known in the art. This insulinotropic peptide derivativemay be modified to have a neutral or net negative charge by the removalor substitution of alpha-amino-terminal histidine residues, or removalof alpha-carbon.

More preferably, the insulinotropic peptide derivative with a modifiedN-terminal charge according to the present invention may include aderivative prepared by removing the amino group of the N-terminalhistidine of the insulinotropic peptide (desamino-histidyl derivative),a derivative prepared by substitution of the N-terminal amino group witha hydroxyl group (beta-hydroxyimidazopropionyl derivative), a derivativeprepared by modification of the N-terminal amino group with two methylgroups (dimethyl-histidyl derivative), a derivative prepared bysubstitution of the N-terminal amino group with a carboxyl group(beta-carboxyimidazopropionyl derivative), or a derivative prepared byremoval of the alpha-carbon of a N-terminal histidine residue to leaveonly the imidazoacetyl group (imidazoacetyl derivative). Any kind of theinsulinotropic peptide derivative with a modified N-terminal amino groupmay be within the scope of the present invention as long as itsN-terminal positive charge can be modified to a neutral or net negativecharge.

The insulinotropic peptide derivative with a modified N-terminal chargeas described above may be represented by the following structures:

Furthermore, the insulinotropic peptide derivative with a modifiedN-terminal charge according to the present invention may include aderivative in which the C-terminal carboxyl group of thedesamino-histidyl derivative with removal of the N-terminal amino groupis substituted with propylaminde as described above.

The insulinotropic peptide derivative with a modified N-terminal chargeas described above can be represented by the following structure:

Still more preferably, the insulinotropic peptide derivative accordingto the present invention may be a derivative in which the N-terminalhistidine residue of GPL-1, exendin-4, exendin-3, oxyntomodulin, GIP,its analogue or a fragment thereof is substituted withdesamino-histidyl, dimethyl-histidyl, beta-hydroxy imidazopropionyl,4-imidazoacetyl, or beta-carboxy imidazopropionyl, thereby modifying itsN-terminal charge.

In an aspect, the insulinotropic peptide derivative with a modifiedN-terminal charge according to the present invention may be representedby the following Formula 1:

R1-X—R2  <Formula 1>

wherein R1 is selected from the group consisting of desamino-histidyl,dimethyl-histidyl, beta-hydroxy imidazopropionyl, 4-imidazoacetyl, andbeta-carboxy imidazopropionyl;

R2 is —NH₂ or —OH,

X isAla-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-Ser-Tyr-Leu-Glu-Gly-Gln-Ala-Ala-Lys-Glu-Phe-Ile-Ala-Trp-Leu-Val-Lys-Gly-Arg-Gly(SEQ ID NO: 7);

Ser-Asp-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser(SEQ ID NO: 8);

Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser(SEQ ID NO: 9); or

Ser-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu-Met-Asn-Thr-Lys-Arg-Asn-Arg-Asn-Asn-Ile-Ala(SEQ ID NO: 10).

In a preferred embodiment of the present invention, the insulinotropicpeptide derivative is a derivative with modification of the N-terminalcharge of exendin-4, and it may be selected from the group consisting ofdesamino-histidyl-exendin-4 (DA-exendin-4) prepared by removing theN-terminal amino group of exendin-4; beta-hydroxyimidazopropionyl-exendin-4 (HY-exendin-4) prepared by substituting theN-terminal amino group of exendin-4 with a hydroxyl group;beta-carboxyimidazopropionyl-exendin-4 (CX-exendin-4) prepared bysubstituting the N-terminal amino group of exendin-4 with a carboxylgroup; dimethyl-histidyl-exendin-4 (DM-exendin-4) prepared by modifyingthe N-terminal amino group of exendin-4 with two methyl residues; andimidazoacetyl-exendin-4 (CA-exendin-4) prepared by removing thealpha-carbon of histidine, which is the first amino acid of exendin-4.

Further, the insulinotropic peptide derivative of the present inventionmay be one in which the N-terminal histidine residue of GLP-1,exendin-4, exendin-3, oxyntomodulin, GIP, its analogue, or a fragmentthereof is substituted with desamino-histidyl, and the C-terminalcarboxyl group thereof is substituted with 3-amino propylamide.

In another aspect, the insulinotropic peptide derivative with a modifiedN-terminal charge may include DA-exendin-4-propyl-amide prepared byremoving the N-terminal amino group of exendin-4 while substituting theC-terminal carboxyl group of desamino-histidyl-exendin-4 (DA-exendin-4)with 3-amino propylamide.

The above derivatives are those in which the alpha-amino group of theamino-terminal histidine residue is removed or substituted or thealpha-carbon is removed. The amino acid sequences are not particularlylimited as long as the physiological activities of the derivatives aremaintained.

Like the exendin-4 derivative, such substitution or removal may beapplied even to the N-terminal end of other types of insulinotropicpeptides, e.g., exendin-3, GLP-1, oxyntomodulin, and GIP. This may beapplied even to their analogues and fragments thereof as long as theirinsulinotropic activities are maintained.

The insulinotropic peptide derivative with a modified N-terminal chargeaccording to the present invention can be rapidly dissociated from theGLP-1 receptor, thus preventing clearance of the insulinotropic peptideand reducing desensitization.

Also, the insulinotropic peptide derivative with a modified N-terminalcharge in accordance with the present invention exhibits increasedinsulinotropic activity and in-vivo blood glucose level-loweringactivity due to a change of the binding activity with the GLP-1 receptoras compared to a native insulinotropic peptide.

The insulinotropic peptide derivative according to the present inventioncan have increased insulinotropic activity as compared to a nativeinsulinotropic peptide and exhibit excellent in-vivo glucoselevel-lowering activity because the N-terminal charge of theinsulinotropic peptide is changed to a neutral or net positive charge tocause a change in the binding activity with the GLP-1 receptor.

In an embodiment of the present invention, the insulinotropic peptidederivative, in which the positive charge on the N-terminal amino acid ofthe insulinotropic peptide is modified to a neutral or net negativecharge, has a higher dissociation constant (Kd) from the GLP-1 receptorthan that of the native insulinotropic peptide. Accordingly, it has beenconfirmed that frequent binding and dissociation with the GPL-1 receptorcan be repeated (see Example 1). Moreover, it has been confirmed thatthe insulinotropic peptide derivative, in which the N-terminal charge ofthe insulinotropic peptide is modified, exhibited an about two-foldincrease in insulinotropic activity compared to the nativeinsulinotropic peptide, in which the N-terminal charge of theinsulinotropic peptide is not modified (see Example 2). In addition, theinsulinotropic peptide derivative, in which the N-terminal charge of theinsulinotropic peptide is modified, exhibited a five-fold increase inglucose level-lowering activity in diabetic animal models (db/db mice)compared to the native insulinotropic peptide (see Example 3).

Accordingly, it can be seen that the insulinotropic peptide derivative,in which the positive charge on the N-terminal amino acid of theinsulinotropic peptide is modified according to the present invention,has an increased dissociation constant from GLP-1, i.e., an increase indissociation from a GLP-receptor, thus showing excellent stability inblood and insulinotropic activity.

As described above, it has been first found by the present applicationthat, if the N-terminal charge of the insulinotropic peptide is modifiedto a neutral or net negative charge, the binding activity with theGLP-receptor, particularly the dissociation from the above receptor canbe increased, thus leading to increased biological activity of theinsulinotropic peptide. Accordingly, the excellent stability in bloodand insulinotropic activity of the insulinotropic peptide derivativeaccording to the present invention will be useful to maximize the effectof the treatment of type 2 diabetes.

In another embodiment, the present invention provides a pharmaceuticalcomposition for the treatment of diabetes containing as an activeingredient the insulinotropic peptide derivative, in which theN-terminal charge is modified.

The description of the insulinotropic peptide derivative with a modifiedN-terminal charge is as described above.

The insulinotropic peptide derivative with a modified N-terminal chargeaccording to the present invention has higher insulinotropic activityand glucose level-lowering activity as compared to the nativeinsulinotropic peptide, and thus it can be used as an excellenttherapeutic drug for diabetes.

The pharmaceutical compositions for the treatment of diabetes mellitusaccording to the present invention can be administered to a subject inneed thereof to effectively treat diabetes.

Accordingly, a method for treating diabetes in a subject includesadministering a therapeutically effective amount of the insulinotropicpeptide derivative with modification of the N-terminal charge aspreviously described, to a subject in need thereof.

The term “treatment” as used herein refers to all of the actions bywhich the symptoms of diabetes have taken a turn for the better or beenmodified favorably by administration of the insulinotropic peptidederivative with a modified N-terminal charge or the pharmaceuticalcomposition containing the same.

The term “administration” as used herein refers to introduction of apredetermined amount of the insulinotropic peptide derivative with amodified N-terminal charge or the pharmaceutical composition containingthe same into a subject by a certain suitable method. The drug may beadministered via any of the common routes, as long as it is able toreach a desired tissue. For example, the modes of administration includeintraperitoneal, intravenous, intramuscular, subcutaneous, intradermal,oral, topical, intranasal, intrapulmonary and intrarectaladministration, but are not limited thereto. However, since peptides aredigested upon oral administration, the composition for oraladministration should be coated or formulated for protection againstdegradation in the stomach. Preferably, the composition may beadministered in an injectable form. In addition, the pharmaceuticalcomposition may be administered using a certain apparatus capable oftransporting the active ingredients into a target cell.

Further, the pharmaceutical composition including the derivative of thepresent invention may include a pharmaceutically acceptable carrier. Fororal administration, the pharmaceutically acceptable carrier may includea binder, a lubricant, a disintegrant, an excipient, a solubilizer, adispersing agent, a stabilizer, a suspending agent, a coloring agent, aflavoring agent, etc. For injection preparations, the pharmaceuticallyacceptable carrier may include a buffering agent, a preserving agent, ananalgesic, a solubilizer, an isotonic agent, a stabilizer and the like.For preparations for topical administration, the pharmaceuticallyacceptable carrier may include a base, an excipient, a lubricant, apreserving agent, etc.

The pharmaceutical composition of the present invention may beformulated into a variety of dosage forms in combination with theaforementioned pharmaceutically acceptable carriers. For example, fororal administration, the pharmaceutical composition may be formulatedinto tablets, troches, capsules, elixirs, suspensions, syrups, orwafers. For injection preparations, the pharmaceutical composition maybe formulated into an ampule as a single-dose form or a multi-dosecontainer. The pharmaceutical composition may also be formulated intosolutions, suspensions, tablets, pills, capsules, and long-actingpreparations.

On the other hand, examples of the carrier, the excipient and thediluent suitable for formulations may include lactose, dextrose,sucrose, sorbitol, mannitol, xylitol, erythritol, maltitol, starch,acacia, alginate, gelatin, calcium phosphate, calcium silicate,cellulose, methylcellulose, microcrystalline cellulose,polyvinylpyrrolidone, water, methylhydroxybenzoate,propylhydroxybenzoate, talc, magnesium stearate and mineral oils. Inaddition, the pharmaceutical formulations may further include fillers,anti-coagulating agents, lubricants, humectants, flavors, andantiseptics.

The insulinotropic peptide derivative with a modified N-terminal chargeaccording to the present invention and the pharmaceutical compositioncontaining the same is administered in a therapeutically effectiveamount. In the present invention, the term “therapeutically effectiveamount” refers to an amount sufficient to treat the disease at areasonable benefit/risk ratio applicable for medical treatment, and thelevel of the effective amount may be determined depending on factorsincluding type of patient's disease, severity of illness, drug activity,drug sensitivity, administration time, administration route, dissolutionrate, length of treatment, the drug to be used simultaneously, andelements well-known in other medical fields. The insulinotropic peptidederivative with a modified N-terminal charge according to the presentinvention and the pharmaceutical composition containing the same may beadministered as an individual therapeutic agent or in combination withother therapeutic agent(s), or sequentially or simultaneously withconventional therapeutic agent(s), or it may be subjected to single ormultiple administration. In view of all the above elements, it isimportant to administer an amount that can achieve the maximum effectwith the minimum amount without adverse effects, which can be readilydetermined by one skilled in the art.

The administration frequency and dose of the pharmaceutical compositionaccording to the present invention are determined by the type ofdiseases to be treated, administration routes, the patient's age,gender, weight, and disease severity as well as by the types of the drugas an active component. Since the pharmaceutical composition of thepresent invention has excellent durations of in-vivo efficacy and titer,it can significantly reduce the administration frequency and dose of thepharmaceutical drugs.

In the present invention, the “subject” includes humans, monkeys, cows,horses, sheep, pigs, chickens, turkeys, quails, cats, dogs, mice, rats,and guinea pigs, but is not limited thereto. In an embodiment, thesubject refers to a mammal, and in another embodiment, the subjectrefers to a human.

MODE FOR INVENTION

Hereinafter, the present invention will be described in more detail withreference to Examples. However, these Examples are for illustrativepurposes only, and the invention is not intended to be limited to theseExamples.

Example 1: Comparison of the Binding Activity of GLP-1 Receptor and theInsulinotropic Peptide Derivative with a Modified N-Terminal Charge

The binding activity of the GLP-1 receptor and the insulinotropicpeptide derivative with a modified N-terminal charge were measured usinga surface plasmon resonance (SPR) apparatus (BIACORE 3000, GEHealthcare). In this case, as the insulinotropic peptide derivative witha modified N-terminal charge, CA-exendin-4, DA-exendin-4, HY-exendin-4,and DA-exendin-4-propyl-amide were used.

CA-exendin-4 is a derivative prepared by removing the alpha-carbon ofthe N-terminal histidine residue of exendin-4; DA-exendin-4 is aderitivate prepared by removing the N-terminal amino group of exendin-4;HY-exendin-4 is a derivative prepared by substituting the N-terminalamino group of exendin-4 with a hydroxyl group; andDA-exendin-4-propyl-amide is a derivative prepared by removing theN-terminal amino group of exendin-4 while substituting the C-terminalcarboxyl group with 3-amino propylamide. In addition, a native exendin-4(exenatide: BYETTA®) was used as a control. Exendin-4 derivatives with amodified N-terminal charge were synthesized by American PeptideCorporation, and the native exendin-4 was obtained from AmylinPharmaceuticals.

The GLP-1 receptor was expressed from CHO-DG44 cells in hGLP-1R/GSTform. The expressed hGLP-1R/GST was immobilized to a CM5 chip by aminecoupling. To the hGLP-1R/GST-immobilized CM5 chip, the insulinotropicpeptide derivatives with a modified N-terminal charge were diluted byconcentration and then added to determine the binding activity with theGLP-1 receptor. The binding activity between the insulinotropic peptidederivatives with a modified N-terminal charge and the receptor wasanalyzed according to a 1:1 Langmuir fitting model and the results areshown in FIGS. 1a to 1e and Table 1 below.

TABLE 1 N-terminal charge at Ka (1/Ms, kd (1/s, Sample pH 7.4 ×10⁵)×10⁴) K_(D) (nM) Native exendin-4 Positive 3.70 ± 0.06 5.26 ± 0.11  1.4± 0.05 charge CA-exendin-4 Neutral 1.20 ± 0.11 31.5 ± 0.56 26.3 ± 2.08DA-exendin-4 charge 1.13 ± 0.08 36.5 ± 1.40 32.2 ± 1.89 DA-exendin-4-1.04 ± 0.11 33.5 ± 1.40 32.6 ± 4.17 propyl-amide HY-exendin-4 0.90 ±0.07 38.3 ± 1.92 42.7 ± 4.10

As shown in Table 1 and FIGS. 1a through 1e , it has been confirmed thatthe N-terminal end of the native exendin-4 has a positive charge,whereas exendin-4 derivatives, where this charge is changed to a neutralcharge, exhibited a significantly increased dissociation constant (kd).These results show that that more frequent coupling/dissociation canoccur repeatedly between the GLP-1 receptor and the insulinotropicpeptide derivative with a modified N-terminal charge.

These pharmacokinetic changes in the GLP-1 receptor can preventclearance of the insulinotropic peptide derivative by the receptor andmake desensitization less likely to occur. Therefore, the insulinotropicpeptide derivative with a modified N-terminal charge is advantageous forincreasing the stability in blood.

Example 2: Measurement of Insulinotropic Activity of the InsulinotropicPeptide Derivative with a Modified N-Terminal Charge

The insulinotropic activities of the insulinotropic peptide derivativeswith a modified N-terminal charge were compared in RINm5F cells. RINm5Fcells were thawed, and subcultured at least once, followed byinoculation into a 96-well plate at a density of 1×10⁵ cells/well with aculture medium containing FBS (Gibco, #11082). Then, the cells werecultured in a 5% CO₂ incubator at 37° C. for 48 hours. For themeasurement of the insulinotropic activities, the culture medium ofRINm5F cells was replaced with a fresh medium containing 0.5% FBS, andthen incubated for 1 hour.

Each of the insulinotropic peptide derivatives with a modifiedN-terminal charge and a native exendin-4 (exenatide: BYETTA®) wasdiluted with a culture medium containing 0.5% FBS and glucose to yieldconcentrations from 10 nM to 0.001 nM. At this time, the culture mediumnot containing exendin-4 was used as a control group. The culture mediumof RINm5F cells was removed, and the prepared samples were addedthereto, followed by culturing in a 5% CO₂ incubator at 37° C. for 1hour. Then, the medium was recovered from each well. A rat insulin ELISAkit (Mercodia) was used to determine the insulin concentrations of therecovered medium, and the results are shown in FIG. 2 and Table 2.

TABLE 2 Ratio of maximum insulin Sample secretion to control groupInsulinotropic peptide 198.9% derivatives with a modified N-terminalcharge Native exendin-4 159.0%

As shown in Table 2 and FIG. 2, it was found that the insulinotropicpeptide derivatives with a modified N-terminal charge according to thepresent invention exhibited about 1.25-fold higher insulinotropicactivity than native exendin-4 at the same concentration range.

Example 3. Comparison of In-Vivo Efficacy of the Insulinotropic PeptideDerivative with a Modified N-Terminal Charge

To measure in-vivo efficacy of the insulinotropic peptide derivativeswith a modified N-terminal charge, their blood glucose lowering effectwas measured in a diabetic animal model, as compared with nativeexendin-4. The db/db mice (Jackson Lab, 10-12 week-old) were made tofast for 2 hours, and then the insulinotropic peptide derivatives with amodified N-terminal charge and exendin-4 (exenatide: BYETTA®) wereadministered at an amount of 0.01-1000 mcg/kg via a subcutaneous route,respectively. At this time, a vehicle was similarly administered as acontrol group, and % change of blood glucose vs. the vehicle wascalculated at each concentration. After 1 hour, blood samples werecollected from a tail blood vessel to measure blood glucose levels usinga glucometer. At each concentration, the ED₅₀ for the blood glucoselevel-lowering effect vs. the vehicle was calculated using the Prismprogram.

TABLE 3 Sample ED₅₀ (mcg/kg) R² Insulinotropic peptide 2.30 0.99derivatives with a modified N- terminal charge Native exendin-4 9.920.98

As shown in Table 3 and FIG. 3, it was found that the insulinotropicpeptide derivatives with a modified N-terminal charge according to thepresent invention exhibited an about 5-fold higher blood glucoselevel-lowering effect than native exendin-4 in the diabetic animalmodel.

From the above-described results, it can be seen that the insulinotropicpeptide derivative with a modified N-terminal charge according to thepresent invention can be rapidly dissociated from the GLP-1 receptor dueto an increase in the dissociation constant with the GLP-1 and thusexhibits stability in blood, causing increased insulinotropic activityand a blood glucose level-lowering effect. Therefore, the insulinotropicpeptide derivative according to the present invention can be veryeffectively used for the treatment of diabetes.

Based on the above description, it will be understood by those skilledin the art that the present invention may be implemented in a differentspecific form without changing the technical spirit or essentialcharacteristics thereof. Therefore, it should be understood that theabove embodiment is not limitative, but illustrative in all aspects andthat all changes and modifications that are derived from the subjectmatter defined in the claims or equivalents thereof are intended to beembraced in the scope of the present invention.

INDUSTRIAL APPLICABILITY

The insulinotropic peptide derivative with a modified N-terminal chargeaccording to the present invention can be rapidly dissociated from theGLP-1 receptor and thus it can prevent clearance of the insulinotropicpeptide and is less likely to cause desensitization. Also, theinsulinotropic peptide derivative with a modified N-terminal charge inaccordance with the present invention exhibits increased insulinotropicactivity and an in-vivo blood glucose level-lowering effect due to achange of the binding activity with the GLP-1 receptor as compared to anative insulinotropic peptide. Therefore, the insulinotropic peptidederivative according to the present invention can be very effectivelyused for the treatment of diabetes.

1. An insulinotropic peptide derivative, wherein the insulinotropicpeptide derivative is a native insulinotropic peptide having amodification on its N-terminal charge.
 2. The insulinotropic peptidederivative of claim 1, wherein the positive charge on the N-terminalamino group or N-terminal amino acid residue of the nativeinsulinotropic peptide, or its analogue, or a fragment thereof ischemically modified to a neutral or net negative charge.
 3. Theinsulinotropic peptide derivative of claim 2, wherein the N-terminalresidue of the native insulinotropic peptide, or its analogue, or afragment thereof is histidine, and the modification is removal orsubstitution of the alpha-amino group of the histidine residue, orremoval of the alpha-carbon, thereby having a neutral or net negativecharge.
 4. The insulinotropic peptide derivative of claim 3, wherein themodification is at least one selected from the group consisting of:removing the N-terminal amino group of the native insulinotropicpeptide, or its analogue or a fragment thereof; substituting theN-terminal amino group of the native insulinotropic peptide, or itsanalogue or a fragment thereof with a hydroxyl group; modifying theN-terminal amino group of the native insulinotropic peptide, or itsanalogue or a fragment thereof with two methyl groups; substituting theN-terminal amino group of the native insulinotropic peptide, or itsanalogue or a fragment thereof with a carboxyl group; removing thealpha-carbon of the N-terminal histidine residue of the nativeinsulinotropic peptide, or its analogue or a fragment thereof therebyleaving only the imidazoacetyl group; and removing the N-terminal aminogroup of the native insulinotropic peptide, or its analogue or afragment thereof while substituting the C-terminal carboxyl group of thenative insulinotropic peptide, or its analogue or a fragment thereofwith propylamide.
 5. The insulinotropic peptide derivative of claim 4,wherein the N-terminal residue of the native insulinotropic peptide orits analogue or a fragment thereof is substituted with a materialselected from the group consisting of desamino-histidyl,dimethyl-histidyl, beta-hydroxy imidazopropionyl, 4-imidazoacetyl, andbeta-carboxyimidazopropionyl.
 6. The insulinotropic peptide derivativeof claim 4, wherein the N-terminal residue of the native insulinotropicpeptide or its analogue or a fragment thereof is substituted withdesamino-histidyl, and the C-terminal carboxyl group of the nativeinsulinotropic peptide or its analogue or a fragment thereof issubstituted with propylamide.
 7. The insulinotropic peptide derivativeof claim 1, wherein the insulinotropic peptide derivative has a bindingactivity with a GLP-1 receptor.
 8. The insulinotropic peptide derivativeof claim 1, wherein the native insulinotropic peptide derivative isGLP-represented by SEQ ID NO: 1, exendin-4 represented by SEQ ID NO: 2,exendin-3 represented by SEQ ID NO: 3, oxyntomodulin represented by SEQID NO: 5, GIP represented by SEQ ID NO: 6, an analogue thereof, or afragment thereof.
 9. The insulinotropic peptide derivative of claim 8,wherein the native insulinotropic peptide derivative or its analogue isa GLP-1 analogue, and is selected from the group consisting ofArg³⁴-GLP-1(7-37), Gly⁸-GLP-1(7-36)-amide, Gly⁸-GLP-1(7-37),Val⁸-GLP-1(7-36)-amide, Val⁸-GLP-1(7-37), Val⁸Asp²²-GLP-1(7-36)-amide,Val⁸Asp²²-GLP-1(7-37), Val⁸Glu²²-GLP-1(7-36)-amide,Val⁸Glu²²-GLP-1(7-37), Val⁸Lys²²-GLP-1(7-36)-amide,Val⁸Lys²²-GLP-1(7-37), Val⁸Arg²²-GLP-1(7-36)-amide,Val⁸Arg²²-GLP-1(7-37), Val⁸His²²-GLP-1(7-36)-amide,Val⁸His²²-GLP-1(7-37), Val⁸Trp¹⁶Glu²²-GLP-1(7-37),Val⁸Glu²²Val²⁵-GLP-1(7-37), Val⁸Tyr¹⁶Glu²²-GLP-1(7-37),Val⁸Trp¹⁶Glu²²-GLP-1(7-37), Val⁸Leu¹⁶Glu²²-GLP-1(7-37),Val⁸Tyr¹⁸Glu²²-GLP-1(7-37), Val⁸Glu²²His³⁷-GLP-1(7-37),Val⁸Glu²²Ile³³-GLP-1(7-37), Val⁸Trp¹⁶Glu²²Val²⁵Ile³³-GLP-1(7-37),Val⁸Trp¹⁶Glu²²Ile³³-GLP-1(7-37), Val⁸Glu²²Val²⁵Ile³³-GLP-1(7-37), andVal⁸Trp¹⁶Glu²²Val²⁵-GLP-1(7-37).
 10. The insulinotropic peptidederivative of claim 8, wherein the native insulinotropic peptidederivative or its analogue is a ZP-10(Ser³⁸Lys³⁹-exendin-4(1-39)-LysLysLysLysLys-amide), which is anexendin-4 analogue represented by SEQ ID NO:
 4. 11. The insulinotropicpeptide derivative of claim 1, wherein the insulinotropic peptidederivative has a higher dissociation constant (Kd) for the GLP-1receptor compared to the native insulinotropic peptide.
 12. Theinsulinotropic peptide derivative of claim 5, wherein the insulinotropicpeptide derivative is represented by the following Formula 1:R1-X—R2  <Formula 1> wherein R1 is selected from the group consisting ofdesamino-histidyl, dimethyl-histidyl, beta-hydroxy imidazopropionyl,4-imidazoacetyl, and beta-carboxy imidazopropionyl; R2 is —NH₂ or —OH, XisAla-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-Ser-Tyr-Leu-Glu-Gly-Gln-Ala-Ala-Lys-Glu-Phe-Ile-Ala-Trp-Leu-Val-Lys-Gly-Arg-Gly;Ser-Asp-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser;Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser;orSer-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu-Met-Asn-Thr-Lys-Arg-Asn-Arg-Asn-Asn-Ile-Ala.13. The insulinotropic peptide derivative of claim 6, wherein theN-terminal histidine residue of GLP-1, exendin-4, exendin-3,oxyntomodulin, GIP, or an analogue thereof is substituted withdesamino-histidyl, and the C-terminal carboxyl group of GLP-1,exendin-4, exendin-3, oxyntomodulin, GIP, or an analogue thereof issubstituted with propylamide.
 14. The insulinotropic peptide derivativeof claim 12, wherein the insulinotropic peptide is selected from thegroup consisting of desamino-histidyl-exendin-4 prepared by removing theN-terminal amino group of exendin-4; beta-hydroxyimidazopropionyl-exendin-4 prepared by substituting the N-terminal aminogroup of exendin-4 with a hydroxyl group;beta-carboxyimidazopropionyl-exendin-4 prepared by substituting theN-terminal amino group of exendin-4 with a carboxyl group;dimethyl-histidyl-exendin-4 prepared by modifying the N-terminal aminogroup of exendin-4 with two methyl groups; and imidazoacetyl-exendin-4prepared by removing the alpha-carbon of histidine, which is the firstamino acid of exendin-4.
 15. The insulinotropic peptide derivative ofclaim 13, wherein the insulinotropic peptide derivative isDA-exendin-4-propyl-amide prepared by removing the N-terminal aminogroup of exendin-4 and substituting the C-terminal carboxyl group withpropylamide.
 16. A pharmaceutical composition for the treatment ofdiabetes comprising as an active ingredient the insulinotropic peptidederivative as defined in claim
 1. 17. A method for treating diabetescomprising administering a therapeutically effective amount of theinsulinotropic peptide derivative as defined in claim 1 to a subject inneed thereof.